Ormoceras
Encyclopedia
Ormoceras is an actinocerid genus of the family Ormoceratidae which is found in North America from the late Chazyan though the early Cincinnatian of the Middle and Upper Ordovician
, but continued through the Devonian
worldwide.
Ormoceras is a fairly widespread genus representative of the Ormoceratidae with a straight shell, more or less circular in cross section, and a relatively narrow subcentral siphuncle
composed of globular segments in which the radial canals in the endosiphuncular canal system are straight and normal to the central canal. Septal necks are short, narrowly rounded or sharply recurved, but never recumbent. As with most actinocerids, cameral deposits are common.
Ormoceras is derived from Adamsoceras
which has a siphuncle with the same general form but in which the canal system is reticulate as in Wutinoceras. Ormoceras gave rise to Deiroceras early on during the Mohawkian (Middle Ordovician) and slightly later to Troedssonoceras. Ormoceras also gave rise to later genera such as Metarmenoceras from the Lower Devonian of Quebec, either directly or through Cyrtactinoceras of the Silurian
which may also have given rise to the Carbactinoceratidae
of the Carboniferous
.
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
, but continued through the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
worldwide.
Ormoceras is a fairly widespread genus representative of the Ormoceratidae with a straight shell, more or less circular in cross section, and a relatively narrow subcentral siphuncle
Siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...
composed of globular segments in which the radial canals in the endosiphuncular canal system are straight and normal to the central canal. Septal necks are short, narrowly rounded or sharply recurved, but never recumbent. As with most actinocerids, cameral deposits are common.
Ormoceras is derived from Adamsoceras
Adamsoceras
Adamsoceras is an actinocerid of the family Wutinoceratidae, with spheroidal siphuncle segments like Ormoceras but having a reticular canal system like Wutinoceras. Adamsoceras has a slender, gently expanding, orthoconic shell that is slightly broader than high, i.e...
which has a siphuncle with the same general form but in which the canal system is reticulate as in Wutinoceras. Ormoceras gave rise to Deiroceras early on during the Mohawkian (Middle Ordovician) and slightly later to Troedssonoceras. Ormoceras also gave rise to later genera such as Metarmenoceras from the Lower Devonian of Quebec, either directly or through Cyrtactinoceras of the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
which may also have given rise to the Carbactinoceratidae
Carbactinoceratidae
Carbactinoceratidae is a family of extinct cephalopods with external shells that lived around 325 million years ago, during the Carboniferous period. They were the last group of orthocones to attain sizes exceeding one meter in length...
of the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
.